The operation of certain computer equipment can be negatively affected by the presence of environmental hazards, such as airborne contaminants. To prevent this harm from occurring, some sensitive equipment may be housed in an enclosure that is designed to keep out airborne contaminants.
An example of a piece of sensitive equipment housed within a protective enclosure is a hard-disk drive (HDD). An HDD is a non-volatile storage device, which is housed in a protective enclosure, that stores digitally encoded data on one or more circular platters having magnetic surfaces. When an HDD is in operation, each platter is rapidly rotated by a spindle system. Data is read from and written to a platter using a read/write head which is positioned over a specific location on a platter by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a platter. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the space between a read/write head and the surface of a platter must be tightly controlled. To provide a uniform distance between a read/write head and the surface of a platter, an actuator relies on air generated by a self-acting air bearing to support the read/write heads at the proper distance away from the surface of a platter while the platter rotates. A read/write head therefore is said to “fly” over the surface of a platter. That is, the air pulled along by a spinning platter forces the head away from the surface of the platter. When a platter stops spinning, a read/write head must either “land” on the platters or be pulled away.
Very small airborne particles, such as the size of 10 nm to 1000 nm (1 micron), may adhere to the air bearing surfaces of either a read/write head or deposit on the surface of the magnetic platters (disk stack). When the surface of either a read/write head or a platter becomes attached to an airborne particle, it is more likely that a read/write head may not read data properly or may scrape across the surface of a platter, which could grind away the thin magnetic film of the platter and cause data loss and potentially render the HDD inoperable.
As a natural part of the manufacturing process, a certain amount of airborne particles may be introduced into the interior of the enclosure of the HDD. Additionally, during operation, certain parts within the interior of the HDD may rub or bump each other in a manner that causes airborne particles to be released. To remove airborne particles from the interior of a HDD, airborne particle filters may be positioned inside the interior of the enclosure as well as around an air passage in the enclosure used to equalize the pressure between the interior and the exterior of the enclosure. These airborne particle filters are typically situated in a flow of air caused by the rotation of the platters. As the air flows through the airborne particle filters, particles carried by the air may become trapped in the airborne particle filter, thereby cleaning the air.
As the amount of air flowing through an airborne particle filter increases, the number of airborne particles which will be trapped by the airborne particle filter also increases. However, as the rate of the air flow circulating within the enclosure of the HDD increases, the likelihood that the circulating air flow will disturb the operation of the magnetic read/write head also increases. Thus, airborne particle filters are typically designed to collect as much airborne particles from the air as possible without disturbing the proper operation of the magnetic read/write head.
In order to create an appropriate pressure drop across an airborne particle filter to ensure a desired rate of air flow through the airborne particle filter, certain HDDs may employ a bypass channel, which is a channel through which air may flow. While a bypass channel may be helpful in directing the flow of air, a bypass channel can create an aerodynamic disturbance where the bypass channel connects with the shroud which surrounds the platters. Such aerodynamic disturbances are undesirable as they may excite disk vibrations and disturb the operation of the magnetic read/write head or prevent the desired amount of airborne particles to be collected from the airborne particle filters.